Recently, medical diagnosis by use of a capsule endoscope incorporating an image sensor, a light source, and the like in an extremely small capsule has been put to practical use. In the medical diagnosis by use of the capsule endoscope, at first, the capsule endoscope is swallowed by a patient, and while a region to be observed inside a body of a patient (inner wall surface of tracts in the human body) is illuminated by the light source, the region to be observed is shot by the image sensor. Image data thus obtained is wirelessly transmitted to a receiver, and sequentially stored in a recording medium such as a flash memory provided in the receiver. During or after the endoscopy, the image data is retrieved to an information management device such as a work station, and then the image is displayed on the monitor and read for diagnosis.
Number of shooting images by the capsule endoscope per unit time (frame rate) is 2 fps (frame/second), for example. The image shooting is performed for at least eight hours, and the amount of image data stored in the receiver is huge. Therefore, in a case where the image is read out for diagnosis after the endoscopy, when all the shot images are to be read out, it takes a lot of time and work. Conventionally, in order to reduce the burden in the image reading, there are various propositions (for example, see Japanese Patent Translation Publication No. 2004-521662, Japanese Patent Application Laid-open Publication No. 2006-223892, and Japanese Patent Application Laid-open Publication No. 2006-288808).
According to the inventions disclosed in the Japanese Patent Translation Publication No. 2004-521662 and the Japanese Patent Application Laid-open Publication No. 2006-223892, an acceleration sensor and a pressure sensor are used to detect the moving speed of the capsule endoscope in the human body. The frame rate is raised when the moving speed is fast, and the frame rate is lowered when the moving speed is slow. According to the invention disclosed in the Japanese Patent Application Laid-open Publication No. 2006-288808, the strength of a wireless signal transmitted/received between the capsule endoscope and the receiver is detected, and based on the detection result, the position of the capsule endoscope, and then its moving distance are detected. If the moving distance is equal to or less than a threshold value, the operation of the image sensor is halted.
In a case where the moving speed of the capsule endoscope is slow, or the moving distance thereof is equal to or less than a threshold value, there is a possibility that the capsule endoscope remains at the same spot for a long time, and in this case, plural similar images are shot. Accordingly, as disclosed in the Japanese Patent Translation Publication No. 2004-521662 and the Japanese Patent Application Laid-open Publication No. 2006-223892, the frame rate is lowered, or as disclosed in the Japanese Patent Application Laid-open Publication No. 2006-288808, the operation of the image sensor is halted. Thereby, the number of similar images can be decreased, and the burden in the image reading also can be decreased.
While there is a demand for decreasing burden in the image reading as descried above, there is a demand for minutely reading an image of a region to be diagnosed intensively (hereinafter referred to as target region) such as a lesion. Namely, it is expected that the images unnecessary for diagnosis are decreased and the images necessary for diagnosis are increased as much as possible. In view of the above, there is proposed a capsule endoscope capable of shooting images in accordance with a preset time schedule (see Japanese Patent Application Laid-open Publication No. 2005-193066).
In accordance with the Japanese Patent Application Laid-open Publication No. 2005-193066, for example, the time required for the capsule endoscope to pass through an esophagus is as short as within one second in general, and therefore the frame rate is raised when the capsule endoscope is passing through the esophagus. When the capsule endoscope falls into a stomach, the image shooting operation is halted in accordance with the time schedule set previously. Alternatively, when the capsule endoscope is passing through the target region, the frame rate is raised, and after the capsule endoscope has passed through the target region, the frame rate is lowered.
Moreover, there is proposed a capsule endoscope incorporating a memory for storing a parameter for setting the operation condition of each component of the capsule endoscope in which the data stored in the memory can be rewritten wirelessly from the receiver (see Japanese Patent Application Laid-open Publication No. 2004-350963). According to the Japanese Patent Application Laid-open Publication No. 2004-350963, the data stored in the memory is written to correct each of the light amount of the light source and white balance to achieve an appropriate level, and the light amount is changed at each region. Moreover, as in the case of the Japanese Patent Application Laid-open Publication No. 2005-193066, there is described an example that when the capsule endoscope is near the target region, the frame rate is raised, and when the capsule endoscope is away from the target region, the frame rate is lowered.
The diagnosis by use of the capsule endoscope has an advantage (low invasiveness) in that the patient has burden less than that by use of a conventional insertion-type endoscope. Therefore, there is a possibility that the capsule endoscope is used more widely for routine medical examination and past-surgery inspection in the near future. Accordingly, a demand for reading an image of the target region requiring observation, such as a lesion found in the last routine medical examination and a surgery site, more in detail for a short time has been increasing.
However, according to the inventions disclosed in the Japanese Patent Translation Publication No. 2004-521662, the Japanese Patent Application Laid-open Publication No. 2006-223892, and the Japanese Patent Application Laid-open Publication No. 2006-288808, although it is possible to reduce the burden in the image reading, if the moving speed of the capsule endoscope is slow or if the moving distance thereof is equal to or less than the threshold value, when the capsule endoscope is in the target region, the image shooting of the target region is omitted. Therefore, there is a fear that it becomes impossible to read an image of the target region in detail.
Moreover, according to the inventions disclosed in the Japanese Patent Application Laid-open Publication No. 2005-193066 and the Japanese Patent Application Laid-open Publication No. 2004-350963, the frame rate is raised when the capsule endoscope is passing through the target region, and the frame rate is lowered after the capsule endoscope has passed through the target region. However, there is disclosed no examples for specifying the target region. Therefore, as in the case of the Japanese Patent Translation Publication No. 2004-521662, the Japanese Patent Application Laid-open Publication No. 2006-223892, and the Japanese Patent Application Laid-open Publication No. 2006-288808, the demand for reading images of the target region more in detail in a short time can not be achieved.